1. Field of the Invention
The present invention relates in general to projectors which throw images on a screen, and more particularly to projectors of a type which have three image projecting units from which three primary color images are projected to form a visual color image on a screen. More specifically, the present invention is concerned with an improvement in the image projecting unit.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional projector of the above-mentioned type will be described with reference to FIGS. 7 and 8 of the accompanying drawings.
As is seen from FIG. 7, the conventional projector comprises generally three cathode ray tubes (CRT) "a", "b" and "c" on which three primary color images provided by a common image information are displayed respectively, and three lens assemblies "e", "f" and "g" through which the respective three primary color images are projected forward to produce a visual color image on a screen "d". Each cathode ray tube "a", "b" or "c" and its associated lens assembly "e", "f" or "g" thus constitute an image projecting unit "A", "B" or "C".
In order to focus the three primary color images on a common area of the screen "d", the three image projecting units "A", "B" and "C" are suitably inclined with respect to the screen "d", as shown.
Although not shown in FIG. 7, a liquid is placed between each cathode ray tube "a", "b" or "c" and the associated lens assembly "e", "f" or "g" for optically connecting these two devices.
In the projectors of this type, when the size of the screen "d" is changed, the convergence angle ".theta.1", of each lens assembly "e", "f" or "g" should be changed. Thus, it becomes necessary to change the setting angle ".theta.2" of each cathode ray tube "a", "b" or "c" relative to the associated lens assembly "e", "f" or "g".
Japanese Utility Model Provisional Publication 1-115145 shows one of the image projecting units used in the above-mentioned projectors, which is illustrated in FIG. 8 of the accompanying drawings.
As is seen from FIG. 8, the image projecting unit comprises a cathode ray tube 1 having an annular spacer 2 secured thereto. An O-ring 8 is disposed between the cathode ray tube 1 and the spacer 2. Designated by numeral 3 is a rearmost lens of a lens assembly which is arranged in the front of the cathode ray tube 1 and has an annular spacer 4 secured thereto. Another O-ring 9 is disposed between the lens 3 and the spacer 4. Compressed between the spacers 2 and 4 is an annular rubber tube 5 which serves as a part of a liquid container.
Within a circular space 6 defined by the annular rubber tube 5 and the two spacers 2 and 4, there is contained a liquid for achieving an optically good connection between the cathode ray tube 1 and the lens 3.
Designated by numerals 7 and 7 are angle adjusting bolts which extend between peripheral portions of the respective spacers 2 and 4. Each adjusting bolt 7 has a spring disposed thereabout between the spacers 2 and 4.
Thus, when, as is seen from the drawing, one or some of the adjusting bolts 7 and 7 are screwed to advance forward, the setting angle of the cathode ray tube 1 relative to the lens 3 is changed. Under this angled condition, a part of the annular rubber tube 5 is resiliently deformed as shown.
However, due to inherent construction, the usage of the annular rubber tube 5 has hitherto failed to provide the cathode ray tube 1 with a sufficiently large angle relative to the lens 3. In fact, the largest angle of the cathode ray tube 1 relative to the lens 3 is achieved only by strongly compressing one part of the rubber tube 5.